1. Field of the Invention
The present invention relates to a device for use in a rotation-type substrate processing apparatus, in which a substrate is processed with various processing liquids such as cleaning liquid and etching liquid applied onto the substrate The substrate is held and rotated by the device (hereinafter referred to as "a spin head"). The term "substrate" refers to an approximately round-shaped substrate such as a semiconductor wafer or a completely round-shaped substrate such as an optical disk substrate.
2. Description of the Background Art
In a rotation-type substrate processing apparatus for processing substrates such as a semiconductor wafer and a glass substrate for a photomask which must be extremely thoroughly cleaned, maximum possible suppression of a slipping between a substrate and holding members which hold the substrate while the substrate is rotated is necessary. This is because such a slippage causes the substrate surface to be chipped and damaged, and also causes dust to adhere to the substrate surface. This also causes the processing liquid to flow unevenly, which eventually deteriorates the quality of processing. To solve the above problems, various conventional techniques for suppressing a slippage of a spinning substrate have been developed including the one disclosed in Japanese Patent Laid-Open Gazette No. 51-132972 and the one disclosed in Japanese Patent Examined Gazette No. 3-9607 which was filed by the same applicant as in the present application.
In an apparatus according to the former conventional technique, centrifugal arms are attached to a horizontal rotation stage for engagement with the outer edge of a horizontally resting substrate, and pushed against the outer edge of the substrate by a centrifugal force which is created as the horizontal rotation stage rotates. An apparatus according to the latter conventional technique requires movable claws disposed on a horizontal rotation stage for engagement with the outer edge of a horizontally mounted substrate. By moving the claws in a predetermined manner, the substrate is firmly held by the claws at the outer edge under a pressing force acting on the outer edge.
The former conventional technique, however, utilizing centrifugal force to hold the substrate, has a weakness in that suppression of slippage is insufficient when the rotation speed is not high enough, i.e., during an initial period of acceleration and a last period of deceleration of the rotation. The latter technique, on the other hand, always attains suppression of a slippage. However, the latter technique needs a complex structure for the apparatus which requires a high manufacturing cost.